1. Field of the Invention
The present invention relates to a cathode of a magnetron, and in particular to an improved cathode of a magnetron which is capable of increasing the life span of the magnetron, reducing the fabrication cost, and enhancing the performance of the system without using a filament in the conventional art.
2. Description of the Conventional Art
FIG. 1A is a cross-sectional view illustrating a conventional magnetron, and FIG. 1B is a cross-sectional view illustrating a cathode, vanes, and an anode of a conventional magnetron.
As shown therein, a cathode 3 is arranged in the center portion of a yoke 30 (see FIG. 1A) encapsulating inner components of the magnetron.
A cylindrical anode 1 is arranged in the outer portion of the cathode 3, and a plurality of spaced-apart vanes 2 are radially arranged in the anode 1, each outer end of which vanes 2 is fixed to the inner circumferential surface of the anode 1.
In addition, an inner strap ring 9 is arranged on the vanes 2, and an outer strap ring 10 having a greater diameter than that of the inner strap 9 is arranged in the outer side of the inner strap 9.
Here, since the inner strap ring 9 and the outer strap ring 10 are alternately and fixedly engaged to the vanes 2, namely, the vanes 2 to which the inner strap ring 9 is fixedly engaged is not engaged to the outer strap ring 10. Here, the neighboring vanes 2 have a phase difference of 180.degree. from one another and are electrically connected to one another.
The construction of the cathode 3 will now be explained in more detail. As shown in FIG. 1B, an upper end shield 7 for supporting a filament 5 is arranged on the top portion of the filament 5 which is spirally formed so as to effectively radiating electrons.
A rim portion 6 having a larger diameter than the outer diameter of the filament 5 is formed in the upper end shield 7 so as to prevent thermal electrons generated from the filament 5 from escaping to the outside of an interaction space 4.
A lower end shield 8 is arranged in a lower portion of the filament 5 so as to upwardly support the lower portion of the filament 5.
Permanent magnets 12 are arranged in upper and lower portions of the anode 1 as shown in FIG. 1A.
In addition, a resonant portion 14 is formed in a portion surrounded by two neighboring vanes 2 and the anode 1, one side of the resonant portion 14 is open toward the cathode 3, and the resonating frequency of the magnetron is determined in accordance with the resonant frequency.
The operation of the conventional magnetron will now be explained with reference to FIGS. 1A through 1C.
First, a voltage is supplied to the cathode 3, an electric field is generated between the cathode 3 and the vanes 2 in the operational space 4, and an electricmagnetic field is generated in the direction parallel to a center stem 5a of the cathode 3 as shown in FIG. 1B.
Therefore, a high frequency electric field is generated in the LC resonant portion 14 (see FIG. 1C) and is focused to an end portion of each vane 2, and a part of the high frequency electric field is leaked into the interior of the interaction space 4.
In addition, since the inner strap ring 9 and the outer strap ring 10 are alternately engaged to the vanes 2, an electric potential is rapidly changed between the vanes 2, and the electrons radiated from the cathode 3 circles in the interaction space 4 and interacts with the high frequency electric field therein, for thus oscillating microwaves.
In addition, the oscillated microwaves are transferred to the outside of the magnetron through an antenna 11 connected to the vanes 2. Here, since a part of electrons is changed into heat energy, cooling fins 13 (see FIG. 1A) are arranged in the outer portion of the anode 1 so as to prevent the temperature from being increased due to the heat applied thereto.
As shown in FIG. 1A, a filter box 20 having a choke coil 21 and a through type condenser 22 is arranged below the yoke 30 for preventing the leakage of a unnecessary radiating wave which causes an interference with respect to a communication system such as a television, a radio, etc. when an electric wave having a range of 2450 MHz including a range from hundreds of KHz to tens of GHz is generated when a voltage is applied to the system as shown in FIG. 1D.
The conventional magnetron which uses the filament has the following disadvantages.
First, since a current is applied to heat the filament, a filament voltage supply system is additionally necessary, and since the filament becomes activated at a temperature of about 1700.degree., a center lead, a side lead, and other elements which support the filament should be made of an expensive molybdenum having a high melting point.
Second, since about 30 W through 50 W is consumed so as to heat the filament, the efficiency of the magnetron is degraded.
Third, since the heat source of about 1700.degree. C. is transferred to the choke coil through the center lead, the side lead, etc, it is impossible to thermally control the choke coil.
Fourth, it is impossible to effectively cool the magnetron because the resonant space in which the cylindrical anode body and vanes are arranged is heated therein due to the heat from the cathode having a temperature of about 1700.degree. C.
Fifth, since the strength of the filament is very weak, it may be easily damaged by external impact, so that the life span of the magnetron is shortened.
Sixth, since the filament is operated after a lapse of a predetermined time after a voltage is supplied to the filament, electric wave noise occurs during the abnormal operation, thereby degrading the performance of the magnet.